a) Field of the Invention
The invention is directed to a pneumatic sequential control valve for successive aeration and deaeration of two consumers, wherein for purposes of aeration compressed air is initially applied to the first consumer and only subsequently to the second consumer, and for deaeration the compressed air is initially let off from the second consumer and only subsequently from the first consumer. The invention is directed especially to a pneumatic sequential control valve with a valve body in which a cavity is provided which has a longitudinal axis and a control slide which is mounted so as to be displaceable in this cavity in direction of the longitudinal axis of the cavity.
b) Description of the Related Art
Valves with a valve body and a control slide which is displaceably mounted therein have been known for a long time. Further, various embodiment forms of pneumatic sequential control valves for successive aeration and deaeration of two consumers are known, for example, also with a control slide which is mounted in a valve body so as to be displaceable. The known pneumatic sequential control valves are generally relatively complicated constructions and are relatively highly susceptible to problems, so that it is no longer ensured, for example, that the consumers will be controlled in correct sequence.
It is the primary object of the invention to provide a pneumatic sequential control valve which is simple to produce. A further object of the invention is to provide a pneumatic sequential control valve which requires little effort to install in a pneumatic system. A further object of the invention is to provide a pneumatic sequential control valve which has a compact construction but nevertheless allows a high through-flow rate. A further object of the invention is to provide a pneumatic sequential control valve which has the longest possible useful life without maintenance.
These and other objects of the invention which follow from the description are met by a pneumatic sequential control valve according to the invention. A sequential control valve of the type mentioned above according to the invention has the following features:
A valve body with connections for a compressed air line, for a first consumer and for a second consumer, wherein a cavity having a longitudinal axis is provided in the valve body, and a first bore hole extends from the connection for the first consumer to this cavity; further a second bore hole extends from the connection for the second consumer to this cavity; and further a third bore hole extends from the connection for the compressed air line to this cavity; a control slide which is mounted in this cavity so as to be displaceable in direction of the longitudinal axis of the cavity and which has a first end side and a second end side and is displaceable in the first end position and second end position. Said first bore hole and said third bore hole communicate with each other in the first end position of the control slide, and said second bore hole and said third bore hole communicate with each other in the second end position of the control slide. A control space is provided between the first end side of the control slide, at which a piston surface is provided, and the valve body, the volume of the control space being at a minimum in the first end position of the control slide and at a maximum in the second end position of the control slide. This control space communicates with the third bore hole via a choke line. The control slide is biased or pretensioned in direction of its first end position by means of a spring arrangement.
A pneumatic sequential control valve of the type mentioned above can be produced relatively easily. This sequential control valve can make do without direct position-reporting sensors and without additional pressure sensors, so that complicated assembly work can be avoided when installing in the pneumatic system. This sequential control valve can be constructed in such a way that it has a high through-flow in spite of its compact construction, so that a plurality of first and second consumers can also be controlled simultaneously. A pneumatic sequential control valve of this kind functions reliably and can have a very long useful life (for example, more than twenty million switching processes) without requiring maintenance.
With reference to a first, second and third bore hole indicated above and in the following, it is meant that there is at least one such bore hole. In a preferred embodiment example, there are a plurality of such bore holes which are offset relative to one another in circumferential direction to maximize the through-flow of the sequential control valve.
In a preferred embodiment form of the invention, a line is provided in the valve body which connects the third bore hole with the first bore hole and in which a check valve is arranged which closes when the pressure in the first bore hole exceeds the pressure in the third bore hole. By means of this line, pressure is applied to the first consumer when compressed air is applied to the compressed air line even in the second setting of the control slide. Such application of pressure to the first consumer would otherwise have to be carried out in a different manner in order to compensate for pressure losses in the aerated state of the first consumer, for example, by means of an additional switching valve as will be explained in more detail in the description of the drawings.
In a preferred embodiment form of the invention, a line is provided which connects the third bore hole to the second bore hole and in which is arranged a check valve which closes when the pressure in the third bore hole exceeds the pressure in the second bore hole. Without a line of this kind, complete deaeration of the second consumer in the pressureless state of the compressed air line, should such complete deaeration be required, would have to be carried out in a different manner as will be described in more detail in the description of the drawings.
In a preferred initial form of the invention, an additional control space is provided which cooperates with another piston surface of the control slide. When pressure is applied to this additional control space, the control slide is acted upon by a force directed against the pretensioning force of the spring arrangement. A connection line is provided between the additional control space and the second bore hole. This additional control space serves for increased protection against an unwanted change in the state of the control valve in case of a reduction in the system pressure as will follow more clearly in the description of the drawings.
Other advantages and details of the invention are described in the following with reference to the embodiment example shown in the drawing, further objectives of the invention following from this.